The invention relates to a reversible polarity signal transmission circuit operating under digital control. The circuits to be described employ complementary metal oxide semiconductor (CMOS) devices, which are well known in the art, and combine linear amplification with digital switching. The digital switch concept is shown in a design idea titled CMOS SWITCH INVERTS ANALOG SIGNAL UNDER CONTROL OF DIGITAL LOGIC, published in Electronic Design for Dec. 6, 1975, on page 92. CMOS is about ideal for such functions because it is capable of producing circuits that combine both digital and linear functions on a single monolithic integrated circuit (IC) chip.
One of the most common uses of such circuitry is in the implementation of digital-to-analog (D/A) converters and analog-to-digital (A/D) converters which are commonly used in the data acquisition/conversion functions associated with computers. While computers operate digitally the data they handle operates in analog fashion. Such convertors require a reference potential against which potentials to be converted are compared. In many cases a two-polarity reference source is required. It has become a common practice to develop a stable single-polarity reference and to pass it through an inverting buffer when the opposite polarity is required. This can most easily be accomplished using a switched buffer in which a digital control signal determines the output polarity.
While polarity switches are well known, they suffer from some drawbacks. The analog channels must be under digital control, but must remain free of digital switching pulse feed through. Also, the switching action, when reversing signal polarity, should be free of amplifier offset potential effects.